In the next year, the chunk of transit passengers in Delhi is estimated to go up to 18%, said a spokesperson for the Delhi International Airport Ltd, the GMR-controlled consortium that runs the airport.

In the year ended March 31, about 16% of the airport's total 34 million yearly passengers are those in transit, compared to a 13% of 37 million a year earlier and 9% of 28 million in the year before that, according to figures from International Air Transport Association.

In the next year, the chunk of transit passengers in Delhi is estimated to go up to 18%, said a spokesperson for the Delhi International Airport Ltd, the GMR-controlled consortium that runs the airport.

"Surprisingly, international-to-international forms the biggest chunk of our transit passengers," she said, adding the remainder is constituted by fliers transiting between domestic destinations; international to domestic and domestic to international. "While Air India is the biggest contributor to our growth as a hub, we can't discount others such as Jet Airways," she added.

About 10% of Mumbai's 30 million passengers are transit. For other Indian airports the chunk would be much lower. While demand for travel in India has slowed down in tandem with slower economic growth, the growth in Delhi may encourage other foreign airlines to operate through flights via the airport, thus helping India become a stronger connecting point in the global aviation network.

Delhi's growth as a hub is also closely linked to Air India's careful restructuring of its network to use it as a link between its east-west connections or feeding its domestic passengers on to its global network.

Currently, 50% of its 12,000 daily passengers are connecting passengers, said Deepak Brara, director, commercial, at the national carrier. That compares to about 20% of 8,000 passengers in Mumbai.

"While our international operations were fairly scattered earlier, we have now divided our long-haul flights into two banks at the Delhi airport," said Brara. The bigger of the two, or the "10 am bank" are flights to London, Paris, Birmingham, Frankfurt, Sydney and Melbourne which get passengers from Indian cities, the SAARC countries and regional destinations such as Bangkok.

The other one or the "1 am bank" takes mostly local passengers and feeds them on to the airlines' US flights. "So, in the slot which feeds to the Europe network, one flight is fed by passengers from 40-50 flights from local and regional international cities," he adds.

The airline, which recently started direct flights to Sydney, will in October connect Delhi to Rome and Milan and in December to Moscow. Delhi, however, is still far behind airports such as Hong Kong, which, according to industry figures handled 58.2 million passengers last year, out of which 26% were in transit.

London's Heathrow airport handled 70 million passengers, 22% of whom were connecting to other flights. Also, Delhi's growth story as a hub is offset by the fall in absolute number of passengers, as weak macro-economic conditions sap demand for travel.

Also, while Air India has increased focus from Delhi, the imminent tie-up between Jet Airways and Etihad Airways is set to divert a considerable chunk of hub traffic from India on to Abu Dhabi. Etihad plans to pick up a 24% stake in Jet soon.

Jet is fast drawing up a network plan to connect several new cities to Abu Dhabi and increase frequencies from several.